The present invention pertains to the manufacture of roller cone-type rock bits generally in the manner described in U.S. Pat. No. 4,711,143. To facilitate understanding of the present disclosure, U.S. Pat. No. 4,711,143 is expressly incorporated herein by reference.
Briefly, the type of bit in question typically includes a body having a tool joint at one end for connecting the bit to the drill string. The other end is typically trifurcated, i.e. including three legs extending longitudinally generally in the opposite direction of the tool joint, radially displaced from the centerline of the bit, and circumferentially spaced from one another. At its outermost (lowermost in use) end, each leg has a trunnion extending angularly therefrom generally in a radially inward direction, and a respective roller cone is rotatably mounted on each of these trunnions. The number of legs, and thus the number of cones, can, of course, vary, but the vast majority of such rock bits include three legs and three cones.
Traditionally, probably the most common way of forming the main body of such a bit was to form three segments each extending the full length of the bit body, and each including a respective one of the legs as well as a one-third arcuate segment of the tool joint, and then to weld these segments together along joining lines extending generally longitudinally along the bit body. See U.S. Pat. No. 4,276,946 and U.S. Pat. No. 4,187,743 for examples of the forms of such segments.
There had been, however, other techniques in which a portion of the bit body including the tool joint and three stub-like portions of the legs would be formed, the remainders of the legs separately formed, and then joined to the stubs along generally horizontal lines. See U.S. Pat. No. 4,158,973.
Improvements over both of these prior methods were achieved by the technology described in the aforementioned U.S. Pat. No. 4,711,143. A main body member was provided, having a tool joint at one end and a plurality of leg portions or stubs at the other end. Such a body could be of new manufacture, or could be salvaged from a used bit. However, the outer surfaces of the leg stubs to which leg extensions would be welded were not straight horizontal, but were inclined longitudinally inwardly from their radially outer extremities to their inner extremities, preferably lying on a common conical locus. The end surfaces of the leg extensions which were welded to these outer surfaces of the leg stubs were correspondingly shaped.